This invention relates to X-ray tube anode targets and, more particularly, to a metallic alloy for manufacturing a refractory metal anode target.
There is a continuous demand for higher temperature alloys for manufacturing X-ray tube anode targets. This has led to the development of a series of compositions based on molybdenum. The most widely used alloys were and still are molybdenum-titanium-zirconium-carbon (TZM and TZC).
U.S. Pat. Nos. 4,004,174; 4,165,982; 4,657,735 and, 4,780,902 all describe molybdenum based alloys. In U.S. Pat. No. 4,004,174 molybdenum is combined with titanium and/or zirconium to provide an X-ray target structure. In the remaining patents molybdenum is combined with hafnium and carbon, with zirconium also described in the '982 and 902 patents.
Solution-strengthened alloys, such as Mo-W, Mo-V, Mo-Cb, etc. are known in the prior art literature but either do not have enough high temperature strength or create difficulties during manufacturing.
For several years, molybdenum base alloys were being developed, using hafnium and zirconium as alloying elements. All these compositions were considered to be carbide-strengthened alloys and were distinguished one from another by the metal-to-carbon ratio. There were also several attempts to develop theoretical explanations for such alloy designs, but nevertheless it is still not clear what is the best combination. This undoubtedly depends on the application of these alloys, their process history, thermomechanical treatment, etc.
Historically, arc-cast molybdenum alloys, extruded to a certain degree, were the first and are still very important products. During production these alloys undergo considerable amounts of hot work. High deformation (typically 50-95%) takes place during the production of these alloys using swaging, forging, extrusion, etc.
For bimetal X-ray target production via powder metallurgy, where the amount of hot work is limited by the tungsten or tungsten-rhenium layer flowability, forging reduction is in the range of 10-40% which is, typically, the critical level of deformation for alloys with high concentration of alloying elements. That is why commercially available carbide-strengthened alloys do not work satisfactorily or have low process yields due to poor workability during forging.
Therefore, a new series of alloys, where a hybrid structure can be beneficial, is developed herein. In designing this group of alloys the aim and theory is to combine carbide and solution strengthening in one alloy that can provide high temperature properties with good fabricability.